This is a blog detailing the creation/evolution/ID controversy and assorted palaeontological news. I will post news here with running commentary.

Tuesday, November 12, 2013

"Single Evolving Lineage of Early Homo"

This was reported a month or so back. A new fossil has been described from the site of Dmanisi, the 1.8 million year-old site in the Russian republic of Georgia. The skull is almost totally complete and, with associated jaw, is one of the best examples of early Homo in existence. From the abstract of the Lordkipanidze et al1 article:

The Dmanisi sample, which now comprises five crania, provides direct evidence for wide morphological variation within and among early Homo paleodemes. This implies the existence of a single evolving lineage of early Homo, with phylogeographic continuity across continents.

The idea of a single, evolving lineage is the closest you will get to someone admitting that there might be anagenetic speciation going on here. It also suggests a wide range for early Homo that extended from eastern Africa, across the upper coast, and across the strait of Gibraltar. There is evidence of early Homo at Orce, in Spain and Pirro Nord, in Italy from around 1.6 to 1.3 million years ago. No actual hominin remains exist at these sites but the stone tools that have been found found match, generally, those found at Dmanisi. Not a smoking gun but close.

What is intriguing about this is that it is not a huge intellectual leap that is making these hominins move. The newly-described Dmanisi skull has a cranial capacity of 546 cubic centimeters, barely 100 more than the late australopithecines. The morphological diversity also has people interested. From the Science Daily story:

According to [Christophe] Zollikofer, the reason why Skull 5 is so important is that it unites features that have been used previously as an argument for defining different African "species." In other words: "Had the braincase and the face of the Dmanisi sample been found as separate fossils, they very probably would have been attributed to two different species." Ponce de León adds: "It is also decisive that we have five well-preserved individuals in Dmanisi whom we know to have lived in the same place and at the same time." These unique circumstances of the find make it possible to compare variation in Dmanisi with variation in modern human and chimpanzee populations. Zollikofer summarizes the result of the statistical analyses as follows: "Firstly, the Dmanisi individuals all belong to a population of a single early Homo species. Secondly, the five Dmanisi individuals are conspicuously different from each other, but not more different than any five modern human individuals, or five chimpanzee individuals from a given population."

the differences between the East African and Eurasian fossils then could be just regional variation in an evolving polytypic species. This kind of explanation certainly gives the "lumpers" a leg up and, if this explanation is the best one going, calls into our question the splitting that we have applied to other species. Is it, instead, appropriate to sink such taxonomic forms such as Homo heidelbergensis, Homo ergaster, Homo rudolfensis and Homo habilis, all of which exhibit considerable size and shape dimorphism, into one species: Homo erectus which now has taxonomic precedence?

3 comments:

Probably old hat for someone trained in the field, but Joel Duff has an interesting post on the context of the Dmanisi fossils. He often writes on the aspects of a find that should be difficult for YECs to account for, if they paid any attention. http://thenaturalhistorian.com/2013/10/18/geological-context-origin-dmanisi-skull/

Dmanisi's Skull 5 and its kin are a perfect "intermediate population" between the Australopths and later Homo - and thus a dagger in the heart for any kind of Creationism that turns God into a literal Potter making Mud-People.